In order to understand deposition mechanism of iridium thin film by atomic layer deposition, the adsorption of oxygen on Ir(111) surface was studied by use of density functional theory and a periodical slab model. By calculating the adsorption energy and structure of oxygen at four adsorption sites (top, bridge, fcc-hollow and hcp-hollow) on Ir(111) surface, the most stable adsorption site was determined. On this basis, the banding mechanism of 0 and Ir atoms was studied by density of states of oxygen and iridium atoms. Oxygen adsorbed at hcp(parallel) site on Ir(111) surface was the most stable one according to the adsorption energy calculation results. Orbital charge analysis indicate that charge transferred from 5p and 5d orbit to 2p orbit of adsorbed 0 atoms, and 6s orbit of iridium atoms. Meanwhile, density of state study indicated that adsorption of oxygen on Ir(111) surface is mainly due to the interaction between 2p orbit of 0 atoms and 5d orbit of iridium atoms. (C) 2016 Elsevier B.V. All rights reserved.